Studies during the past seven years have ben specifically directed toward elucidating the functional organization of the inner plexiform layer (IPL) by identifying putative transmitters of selected amacrine, interplexiform and ganglion cells and by determining their cellular morphology, spatial organization and circuitry. These studies suggest complex morphological and transmitter/modulator relationships within the IPL. which play critical roles in the processing of visual information within the retina. The major objectives of this application are to: 1) analyze amacrine and ganglion cells with a strong emphasis on selected peptide- and amino acid transmitter-containing cells and 2) begin an analysis of the presumed ON-directionally selective (DS) ganglion cells which terminate upon the medical terminal nucleus of the accessory optic system. This will be accomplished by investigating selected amacrine cell types and ON-DS ganglion cells on the basis of their putative transmitter, transmitter receptor and mRNA expression using light and electron microscopic immunohistochemistry, in situ and blot hybridization nd tissue section receptor autoradiography. Amacrine cell populations will be characterized by quantitative morphological approaches based on immunohistochemical and in vitro intracellular labeling methods. An important goal of these studies is to establish the structural and neurochemical organization of the local IPL circuits that subserve visual processing. The overall goal of this program is to understand visual function by defining the morphological and neurochemical organization of the retina. These studies will aid in the diagnosis and treatment of retinal and choroidal diseases.